This invention relates to methods of fabricating MTJ cells with better thermal endurance and with improved temperature stability.
Magnetic random access memory (MRAM) devices are based on the integration of semiconductor circuits with magnetic tunneling junction (MTJ) type of magnetic material. Additional information as to the fabrication and operation of MTJ cells can be found in U.S. Pat. No. 5,702,831, entitled xe2x80x9cMulti-Layer Magnetic Tunneling Junction Memory Cellsxe2x80x9d, issued Mar. 31, 1998, and incorporated herein by reference. Normal semiconductor processing sometimes requires processing temperatures as high as 400xc2x0 C. or above. Materials presently used in MTJ cells are typically not stable above 300xc2x0 C. and cannot withstand these high temperatures without substantial damage or degradation of the operating characteristics. It is thus desirable to have MTJ material that endures these kinds of high processing temperatures. Otherwise low temperature special processing modules may have to be developed. In some special circumstances this may be feasible. But it definitely increases the cost of producing the MRAM chips or devices if special low temperature processing modules are required.
Also, depending on when the MTJ layer can be inserted in the normal CMOS flow, the size of the memory cell is different. The earlier in the CMOS flow the MTJ layer can be inserted, the smaller the size of the memory cell, since the minimum dimension becomes larger as the number of layers in the CMOS process increases. Thus, it is desirable to have thermally endurable MTJ material that can be inserted earlier in a CMOS flow, so that memory cell size can be smaller. With smaller cell size, the memory density will be higher and the memory will cost less.
A further problem with the integration of MTJ cells with semiconductor circuits in normal semiconductor manufacturing processes, such as CMOS and the like, is the diffusion of common metal electrodes, such as aluminum and aluminum alloy metals, into the magnetic layers during the high heat steps of the process. Upon diffusion of the aluminum into the magnetic layers, operating characteristics of the MTJ cell can be substantially reduced or the cell can be completely inoperative. Many applications of MTJ cells, including memory cells, field sensors, such as disk read heads, and other magnetic-electronic hybrid systems, would benefit from improved MTJ thermal endurance.
Accordingly it is highly desirable to provide a method of fabricating MTJ cells with better thermal endurance and with improved temperature stability, and to provide the resulting apparatus.